1. Field of the Invention
The present invention is directed, in general, to wireless communication systems and, more specifically, to multiplexing control and data information in Single-Carrier Frequency Division Multiple Access (SC-FDMA) communication systems.
2. Description of the Related Art
The present invention considers the transmission of positive or negative acknowledgement signals (ACK or NAK, respectively), channel quality indicator (CQI) signals, precoding matrix indicator (PMI) signals, and rank indicator (RI) signals together with data information signals in a SC-FDMA communications system and is further considered in the development of the 3rd Generation Partnership Project (3GPP) Evolved Universal Terrestrial Radio Access (E-UTRA) Long Term Evolution (LTE). The invention assumes the uplink (UL) communication corresponding to the signal transmission from mobile user equipments (UEs) to a serving base station (Node B). A UE, also commonly referred to as a terminal or a mobile station, may be fixed or mobile and may be a wireless device, a cellular phone, a personal computer device, a wireless modem card, etc. A Node B is generally a fixed station and may also be referred to as a base transceiver system (BTS), an access point, or other terminology. Any combination of ACK/NAK, CQI, PMI, and RI signals may also be jointly referred to as uplink control information (UCI) signals.
The ACK or NAK signal is associated with the application of hybrid automatic repeat request (HARQ) and is in response to the correct or incorrect, respectively, data packet reception in the downlink (DL) of the communication system, which corresponds to signal transmission from the serving Node B to a UE. The CQI signal transmitted from a reference UE is intended to inform the serving Node B of the channel conditions the UE experiences for signal reception in the DL, enabling the Node B to perform channel-dependent scheduling of DL data packets. The PMI/RI signals transmitted from a reference UE are intended to inform the serving Node B how to combine the transmission of a signal to the UE from multiple Node B antennas in accordance with the multiple-input multiple-output (MIMO) principle. Any one of the possible combinations of ACIUNAK, CQI, PMI, and RI signals may be transmitted by a UE in the same transmission time interval (TTI) with data transmission or in a separate TTI without data transmission. The present invention considers the former case.
The UEs are assumed to transmit UCI and/or data signals over a TTI corresponding to a sub-frame. The physical channel carrying the data transmission and, if any, the UCI transmission is referred to as a physical uplink shared channel (PUSCH).
FIG. 1 illustrates a sub-frame structure assumed in the exemplary embodiment of the invention. The sub-frame 110 includes two slots (120a, 120b). Each slot 120 further includes seven symbols, for example, and each symbol 130 further includes of a cyclic prefix (CP) (not shown) for mitigating interference due to channel propagation effects. The signal transmission in the two slots 120a and 120b may be in the same part, or it may be at two different parts of an operating bandwidth (BW). Furthermore, the middle symbol in each slot carriers transmission of reference signals (RS) 140, also known as pilot signals, which are used for several purposes, such as providing channel estimation for coherent demodulation of the received signal, for example. The transmission BW includes frequency resource units, which will be referred to as resource blocks (RBs). In an exemplary embodiment, each RB includes 12 sub-carriers, and UEs are allocated a multiple N of consecutive RBs 150 for PUSCH transmission. A sub-carrier may also be referred to as a resource element (RE).
An exemplary block diagram of transmitter functions for SC-FDMA signaling is illustrated in FIG. 2. Coded CQI bits and/or PMI bits 205 and coded data bits 210 are multiplexed 220. If ACK/NAK bits also need to be multiplexed, data bits are punctured to accommodate ACK/NAK bits (230). The Discrete Fourier Transform (DFT) of the combined data bits and UCI bits is then obtained (240), the sub-carriers 250 corresponding to the assigned transmission BW are selected (255), the Inverse Fast Fourier Transform (IFFT) is performed 260, and finally the cyclic prefix (CP) 270 and filtering 280 are applied to the transmitted signal 290. For brevity, additional transmitter circuitry, such as digital-to-analog converter, analog filters, amplifiers, and transmitter antennas are not illustrated. Also, the encoding process for the data bits and the CQI and/or PMI bits, as well as the modulation process for all transmitted bits, are omitted for brevity.
At the receiver, reverse (complementary) transmitter operations are performed as conceptually illustrated in FIG. 3 where the reverse operations of those illustrated in FIG. 2 are performed. After an antenna receives the radio-frequency (RF) analog signal and after further processing units (such as filters, amplifiers, frequency down-converters, and analog-to-digital converters), which are not shown for brevity, the digital received signal 310 passes through a time windowing unit 320, and the CP is removed (330). Subsequently, the receiver unit applies an FFT 340, selects the sub-carriers 350 used by the transmitter (355), applies an Inverse DFT (IDFT) 360, extracts the ACK/NAK bits and places respective erasures for the data bits (370), and de-multiplexes (380) the data bits 390 and CQI/PMI bits 395. As for the transmitter, well known receiver functionalities such as channel estimation, demodulation, and decoding are not shown for brevity and are not considered material for purposes of explanation of the present invention.
PUSCH transmission from a UE may be configured by the Node B through the transmission of an UL scheduling assignment (SA) or through higher layer signaling to the reference UE. In either case, in order to limit the overhead associated with the setup of the PUSCH transmission and to maintain the same size of the UL SA or the higher layer signaling, regardless of the UCI presence in the PUSCH, only parameters associated with data transmission are assumed to be informed by the Node B to the reference UE. Parameters associated with potential UCI transmission, namely the resources allocated to UCI transmission, in the PUSCH are not specified.
UCI bits usually require better reception reliability than data bits. This is primarily because HARQ typically applies only to data and not to UCI. Additionally, UCI bits may require different reception reliability depending on their type. For example, the target bit error rate (BER) for ACK/NAK bits is typically much lower than that of CQI/PMI bits as, due to their small number, the ACK/NAK bits are protected through repetition coding while more powerful coding methods are applied to CQI/PMI bits. Moreover, erroneous reception of ACK/NAK bits has more detrimental consequences to the overall quality and efficiency of the communication than erroneous reception of CQI/PMI bits.
Therefore, there is a need to determine the parameters for the transmission of UCI signals in the PUSCH based on the parameters for the transmission of data signals in the PUSCH. Further, there is a need to provide different reception reliability for the different types of UCI signals in the PUSCH. Additionally, there is a need to minimize the signaling overhead for determining the parameters for the transmission of different types of UCI signals in the PUSCH.